| Hair follicle | |
|---|---|
 Hair follicle | |
 A photograph of hair on a human arm emerging from follicles | |
| Details | |
| System | Integumentary system |
| Artery | Supratrochlear, supraorbital, superficial temporal, occipital |
| Vein | Superficial temporal, posterior auricular, occipital |
| Nerve | Supratrochlear, supraorbital, greater occipital, lesser occipital |
| Lymph | Occipital, mastoid |
| Identifiers | |
| Latin | folliculus pili |
| MeSH | D018859 |
| TA98 | A16.0.00.023 |
| TA2 | 7064 |
| TH | H3.12.00.3.01034 |
| FMA | 70660 |
| Anatomical terminology | |
The hair follicle is an organ found in mammalian skin.[1] It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides, and immune cells.[1] This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some newborn babies.[1] The process of hair growth occurs in distinct sequential stages: anagen is the active growth phase, catagen is the regression of the hair follicle phase, telogen is the resting stage, exogen is the active shedding of hair phase and kenogen is the phase between the empty hair follicle and the growth of new hair.[1]
The function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine. Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body.[1] For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is often used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair also provides protection from UV sun rays and is an insulator against extremes of hot and cold temperatures.[1] Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance, length and texture.
There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include alopecia[2] or hair loss, hirsutism or excess hair growth and lupus erythematosus.[3][2]
- ^ a b c d e f Blume-Peytavi, Ulrike (2008). Hair growth and disorders. Berlin: Springer. ISBN 9783540469117. OCLC 272298782.
- ^ a b Erjavec SO, Gelfman S, Abdelaziz AR, Lee EY, Monga I, Alkelai A, Ionita-Laza I, Petukhova L, Christiano AM (Feb 2022). "Whole exome sequencing in Alopecia Areata identifies rare variants in KRT82". Nat Commun. 13 (1): 800. Bibcode:2022NatCo..13..800E. doi:10.1038/s41467-022-28343-3. PMC 8831607. PMID 35145093.
- ^ Gilhar, Amos; Etzioni, Amos; Paus, Ralf (2012-04-19). "Alopecia areata". The New England Journal of Medicine. 366 (16): 1515–1525. doi:10.1056/NEJMra1103442. ISSN 1533-4406. PMID 22512484. S2CID 5201399.